European Journal of Solid State and Inorganic Chemistry最新文献

Synthesis and complete structural characterization by X-ray diffraction, DTA, GTA and IR are given for a new cyclohexaphosphate: (1,6-NH₃C₆H₁₂NH₃)₂ (1-NH₃C₁₀H₇)₂P₆O₁₈.2H₂O. This compound is monoclinic P2₁/c with the following unit-cell parameters: a = 11.861(2)Å, b = 10.104(1)Å, c = 19.664(6)Å, β = 96.44(2)°, and Z = 2. The crystal structure has been solved and refined to R = 0.033 using 3928 independent reflections. The atomic arrangement can be described as layer organisation. Layers built by P₆O₁₈ ring anions and water molecules spread in the plans (100). Between these layers are located the organic groups which form hydrogen bonds with oxygen atoms of P₆O₁₈ rings and water molecules. Geometrical characteristics of hydrogen bonds are described. The reported IR study is supported by a delaited theoretical group analysis applied to P₆O₁₈ with D_6h ideal local symmetry.

This paper reports the study of manganese substituted barium fluoroapatite Ba₁₀(P_1−xMn_xO₄)₆F₂ with 0 ≤ × ≤ 0.20. X-rays diffraction investigation indicates that the phosphate-manganate solid solution is complete, at least for this composition range, and follows Vegard's law, while diffuse reflectance and fluorescence spectra confirm that Mn(V) substitutes for P(V) in the barium apatite lattice. EXAFS experiment, at the manganese K edge, performed on the x = 0.2 compound, indicates that the Mn(V)-O distance is 1.73 Å, a much larger value than the P-O distance equal to 1.54 Å.

The (MnO₄)³⁻ vibrational mode frequencies, deduced from the IR and Raman spectra are almost independent of the x value. This indicates that, even at very low manganese content (x = 0.001), the Mn-O distance is also very close to 1.73 Å.

The Mn(V) ion distorts the barium apatite lattice to a large extent when it substitutes for P(V) and imposes its own size to the host sites.

In order to determinate the best crystal growth conditions for KY(WO₄)₂ single-crystals, the investigation of the K₂O-Y₂O₃-WO₃ ternary system was undertaken by the study of three isoplethic sections (K₂W₄O₁₃-Y₂O₃, K₂WO₄-KY(WO₄)₂, K₂W₂O₇-KY(WO₄)₂). The stability domain and the crystallisation field of the compound were then defined: KY(WO₄)₂ is not stoichiometric and melts congruently for the composition 0.81(K₂O.4WO₃)−0.19Y₂O₃ The low temperature phase belongs to the monoclinic system (s.g. C2/c) with a=10.65(1)Å, b=10.34(1)Å, c=7.54(1)Å, β=130.5(1)°. Its crystallisation field was delimited in temperature and composition: an α-KY(WO₄)₂ crystal can grow if x_Y2O3≤0.175.

The new ultraphosphates FeP₄O₁₁, ZnP₄O₁₁ and CdP₄O₁₁ of the CuP₄O₁₁ structure type were synthesized from the corresponding meta- or polyphosphates and P₄O₁₁. Crystallization via the gas phase has been achieved at elevated temperatures using a mixture of P (3 mg) and I₂ (50 mg) as mineralizer. The crystal structure consists of a two-dimensional phosphate network, built from four crystallographically independent 10-membered polyphosphate rings. Each ring contains four secondary and six tertiary PO₄-groups. Two crystallographically independent metal sites showing sixfold coordination by terminal oxygen atoms are located inbetween the phosphate layers. FeO₆-octahedra (2.028(3) Å < d̄ FeO₆ < 2.268(3) Å) and ZnO₆ octahedra (2.002(2) Å < d̄ ZnO₆ < 2.256(2) Å) exhibit slightly larger radial distortion than the CdO₆-octahedra (2.215(7) Å < d̄ CdO₆ < 2.383(3) Å).

The structure of AlVMoO₇ was solved by direct methods from high resolution X-ray powder diffraction data and refined by the Rietveld method. The lattice constants are a=5.3763(3)Å, b=8.1644(3)Å and c=12.7312Å. Space group Pmcn followed from the systematic extinctions and was confirmed by the successful structure solution. Aluminum is octahedrally coordinated by oxygen, whereas vanadium possesses a distorted pyramidal coordination and molybdenum is tetrahedrally coordinated by oxygen atoms. A three dimensional framework structure results from corner and edge connection of the coordination polyhedra. VO₅ pyramids are edge linked to infinite (VO₂⁺)_∞ chains. Therefore, AlVMoO₇ can be classified as a polyvanadate.

The location of Eu³⁺ in α-cordierite, synthesized by a sol-gel route, was investigated by using both site-selective spectroscopy and time-resolved spectroscopy. ⁷F₀ → ⁵D_1,2 excitation and ⁵D₀ → ⁷F_0,1,2 emission spectra were performed at 77 K. The Eu³⁺ ions are distributed in two families : the A family in the structure channels and the B family at (4c) position of D_2h¹⁶ in substitution for Mg²⁺ Four B sub-families were characterized and understood as a difference at the second neighbours, i.e., the four possible occupations of the surrounding tetrahedra by Al and Si. The A family was characterized by anomalous spectra: strong ⁵D₀ → ⁷F₀ transition, high position of the ⁵D₀, ⁵D₁ and ⁵D₂ levels and very large ⁷F_1,2 splittings. By comparison with Eu-doped apatites, in which similar features occur, a predominant Eu-O bonding of covalent character with one of the oxygen ions bordering the channel was assumed. When the annealing temperature increases, Eu³⁺ ions migrate from the channel to the (4c) position.

Thermal Residual Stresses (TRS) induced by cooling down from elaboration process in SiC/ Ti-15-3 composite are evaluated using several models (present in part I). Influence of thermomechanical properties is investigated. It is shown that a small uncertainly on coefficient of thermal expansion has a huge influence on TRS. It is also highlight that the analytical model proposed is a suitable model to obtain quickly information about TRS (rather than the finite element analysis which is a little more accurate but longer too).

Then evolution (relaxation) of the TRS during a fatigue test are investigated. Results show that the TRS decrease rapidly during the first cycles and then become almost constant at about one third of their initial values.

A chain-like zincophosphate [Zn₈(HPO₄)₈(H₂PO₄)₈]•[(C₂H₈N)₈]•4H₂O was obtained at room temperature from a ZnO/P₂O₅/dimethylamine/H₂O mixture. The crystal structure was determined by single crystal X-ray diffraction. The symmetry is monoclinic a=1.26450(7)nm, b=1.08477(5)nm, c=1.46311(4)nm, β=98.793(5)°, space group Cc. The structure consists of chains of zinc-corner-sharing Zn₂P₂O₄ four rings. The negative charge of the chains is compensated by the protonated dimethylamine. The characterization by ³¹P solid state nmr spectroscopy is also reported.

Different models for the calculation of residual stresses induced by cooling down from elaboration process in SiC/Ti-15-3 composite were presented. First of all, an analytical model (derived from those of Eshelby and of Mikata and Taya) already used for ceramic matrix composites is explained. It is a suitable method for elementary composites but we present an extension of this model to real (1D) composites. Then, we also briefly present the finite model using MARC anc MENTAT softwares. Finaly, an analytical model to predict the evolution of TRS during a fatigue test is detailed. The part II of the paper will present the results obtained using all these differents models.

α-Ba₂ZrF₈ is prepared as systematically twinned crystals by hydrothermal synthesis (200°C) or as fine powders either on a sand bath (60°C) (aqueous HF medium) or by solid state reaction at 450°C. Synchrotron radiation was used because of ambiguities in indexations from conventional X-ray (pseudo-hexagonal symmetry). The structure was determined ab initio from synchrotron powder data. Neutron data were used for improving accuracy because some degree of non-stoichiometry was suspected. The cell is orthorhombic, space group Prima, Z = 4, with a = 9.7401(1) Å, b = 5.6147(1) Å and c = 11.8871(1) Å (synchrotron data, 25°C). The final neutron Rietveld refinement led to R_P = 8.4 % and R_B = 3.5 % for the stoichiometric Ba₂ZrF₈ formulation (sand bath sample). The structure is built up from [ZrF₈] bicapped trigonal prisms isolated in a kinked fluorite matrix. The isostructural Pb₂ZrF₈ compound prepared in solution is also examined. An unexpected relationship with NaBaZrF₇ is discussed.